Hierarchical mesoporous/macroporous Co₃O₄ ultrathin nanosheets as free-standing catalysts for rechargeable lithium-oxygen batteries

Hierarchical mesoporous/macroporous Co₃O₄ ultrathin nanosheets were synthesized as free-standing catalysts for rechargeable Li-O₂ batteries. The Co₃O₄ nanosheets were directly grown on nickel foam through a simple hydrothermal reaction, followed by a calcination process. The impact of solvents used in the hydrothermal reaction on the morphology of catalysts has been investigated. The results showed that the prepared Co₃O₄ catalyst synthesized with ethylene glycol and deionized water (1 : 1 in volume) presented a much better electrochemical performance with a capacity of 11 882 mA h g^-1 under a current density of 100 mA g^-1 during the initial discharge and good cycling stability (more than 80 cycles at 200 mA g^-1 with the capacity limited to 500 mA h g^-1). Meanwhile, the charge potential was significantly reduced to ca. 3.7 V. It is interesting to find that the morphology of the discharge product, Li₂O₂ could be changed by controlling the shape of catalysts. The impacts of the hierarchical mesoporous/macroporous nanosheet structure on the performance of Li-O₂ batteries have been discussed.